1. Field of the Invention
The invention relates to uncoated and/or coated sodium percarbonate with improved internal stability and storage stability; and, a process that provides uncoated and/or coated sodium percarbonate with improved internal stability and storage stability.
2. Discussion of the Background
Sodium carbonate peroxohydrate, known commercially as sodium percarbonate, can be used readily to replace perborates as an oxidizing agent in detergents, washing agents, bleaching agents, cleaning agents, and compositions thereof. When compared to chlorine-type agents, sodium percarbonate is slightly inferior in its bleaching effect. However, sodium percarbonate acts more gently, reducing damage to surfaces. Moreover, yellowing is markedly reduced when sodium percarbonate is applied to surfaces comprising synthetic fibers, animal fibers, resin-processed fibers and fibers treated with fluorescent whitening agents. Furthermore, sodium percarbonate is highly soluble in water, with rapid liberation of hydrogen peroxide instead of a poisonous gas, such as chlorine. Therefore, sodium percarbonate is a more gentle oxidizing agent that produces environmentally safe decomposition products, thereby making home and business use of sodium percarbonate as an oxidizing agent very attractive.
Conventional production of sodium percarbonate comprises reacting hydrogen peroxide with sodium carbonate using four different processes: crystallization processes, spray processes, slurry processes, and dry processes. All of which may be adapted for use in mixers, fluid bed reactors, and/or tubular reactors. Such processes may or may not require the presence of stabilizers. Furthermore, granulating aids may be added to the reaction. The above-mentioned processes include a conventional drying step during and/or after the production of sodium percarbonate to reduce moisture to a level sufficient for commercial sodium percarbonate.
The limited stability of sodium percarbonate is caused by the presence of humid air and/or water chemically bound to ingredients or detergents, like zeolites, which cause sodium percarbonate to lose active oxygen during storage.
JP-A 57-42510 describes a process to stabilize sodium percarbonate. The sodium percarbonate at elevated temperature is transferred from a drier to a storage container. Cool air at room temperature and at most 70% humidity is then fed to the storage container. The sodium percarbonate is cooled. Concurrently, the atmosphere in the storage container is replaced by cool air. At the same time the cool air is passed through the sodium percarbonate in the storage container to cool the contents, the water content is reduced. Therefore, the storage life of sodium percarbonate under high atmospheric humidity is elevated, and the tendency for the sodium percarbonate to agglomerate is reduced. However, the stability of sodium percarbonate during storage is needed to improve. Further, this document does not give describe if the process affects the internal stability of sodium percarbonate, nor does it describe how the internal stability may be increased.
EP-Patent 0 396 175 B1 describes another process for the stabilization of sodium perborate monohydrate granules that are stored as loose granules in bulk. Further, the granules are stored in a sealed room at a temperature between 10 and 65° C. In this process, dry air is continuously passed through the stored material throughout its storage. The dew point of the dry air should be below −20° C. and the amount of dry air should be between 1 and 8 Nm3/(h·tNaPb). There are disadvantages to this process because large amounts of dry air having a very low dew point must be passed through the stored material during the overall storage time. Further, there is no indication that the process could be adapted to the storage of sodium percarbonate and there is no indication as to how the internal stability of the stored product is improved by this process.
The general prevailing opinion at a date prior to the present invention is that the active oxygen content of sodium percarbonate decreases as the temperature and action time increases. Therefore, this general prevailing opinion suggested that such conditions should be avoided.